The invention relates to the testing of a structural component of a vehicle, more particularly for the purpose of detecting a crack in such a component. Some structural components of a vehicle, such as an aircraft, are regularly subjected to stresses during the use of the vehicle, which may result in cracks in the components. In order to use the vehicle in adequate conditions of safety, these structural components must be tested in periodic test inspections. In these test inspections, operators check whether a structural component has a crack, and, if so, must estimate certain dimensional characteristics of the crack, particularly its length. For some components, the operators may detect a crack by visual inspection or by moving a sensor over the surface of the component. However, other components are more difficult to access, and such a procedure is not feasible for the detection of a possible crack. In particular, a component to be inspected may be assembled with another component, this other component preventing both visual inspection and the movement of a sensor over the component to be inspected. For example, a structural component 10 shown separately in FIG. 1A has a crack 15. This structural component is assembled with another component 12, shown separately in FIG. 2A. These two components have a set of fastening holes such as the hole marked 21 in the figures. These fastening holes may be used to assemble the components by using fastening means such as bolts or rivets. FIG. 3A shows the structural component 10 and the component 12 assembled together. The component 12 prevents an operator from accessing the structural component 10 to inspect the crack 15. FIGS. 1B, 2B, and 3B show the components 10 and/or 12, in sections taken along the line A-A of FIGS. 1A, 2A and 3A respectively. Some structural components are also difficult for an operator to access: in some cases, the operator may touch a component, but finds it difficult to see it while manipulating the component. It would therefore be desirable to improve the methods of testing structural components, in order to facilitate the detection of a crack in a component which is difficult to access and/or is masked by another component.